This invention relates to a control system for controlling the operation of a compressor in an appliance.
In HVAC systems, the compressor control mechanisms are typically operated off of the 24 Volt secondary winding of a transformer. Compressors need a high line voltage to operate properly. However, line voltages are susceptible to fluctuations, and in particular, going low as a result of poor connections, power failures and peak cooling demand times. A low line voltage causes the compressor to draw more current than necessary, causing it to overheat and burn out. Current compressor configurations do not allow the compressor control mechanisms to monitor the line voltage directly. As a result, there is no means to de-energize the compressor when line voltages get too low in order to prevent the compressor from overheating and burning out. Given the possibility of low line voltage occurrences, the cost for replacing compressors can become significant. Further, a malfunctioning compressor can render the HVAC system inoperable, further, increasing the cost of repair and/or replacement.
Accordingly, there is a need for a compressor control that prevents malfunctioning of the compressor due to fluctuations in line voltage.
A control system for controlling operation of a compressor in a device powered by a first and second line voltage is disclosed. The system comprises a line voltage measurement circuit for measuring a difference in voltage between the first line voltage and the second line voltage before and during the energizing of the compressor, and a controller in communication with the line voltage measurement circuit and the compressor, the controller comprising storage for storing at least a first threshold voltage, a comparator having an output for comparing the voltage difference to the first threshold voltage, and a compressor control mechanism for controlling operation of the compressor based on the output of the comparator. The compressor control comprises a switch for switching the compressor off when the voltage difference is less than the first threshold voltage for a predetermined period of time. The controller storage mechanism also stores a second threshold voltage, and the compressor control mechanism comprises another switch for switching the compressor off when the voltage difference goes below the second threshold voltage. The controller comprises a counter having a count representing a period of time, the count being initialized when the voltage difference is less than the first threshold voltage and incremented for as long as the output of the comparator shows the voltage difference less than the first threshold voltage. The compressor is switched off by the switch of the controller when the period of time equals the predetermined period of time.
The controller also may comprise an indicator for indicating when the compressor is turned off. In another embodiment, a control system comprises a line voltage measurement circuit for measuring a difference in voltage between the first line voltage and the second line voltage before and during the energizing of the compressor, and a controller in communication with the line voltage measurement circuit and the compressor. The controller comprises storage for storing a second threshold voltage, a comparator having an output for comparing the voltage difference to the second threshold voltage, and a compressor control mechanism for controlling operation of the compressor based on the output of the comparator. The compressor control mechanism comprises a switch for switching the compressor off when the voltage difference goes below the second threshold voltage. The controller may further comprise an indicator for indicating when the compressor is turned off.
A method for controlling operation of a compressor in a device powered by a first and second line voltage and having a controller is also disclosed. The method comprises measuring a difference in voltage between the first line voltage and the second line voltage before and during the energizing of the compressor, storing at least a first threshold voltage in the controller, comparing the voltage difference to the first threshold voltage, and controlling operation of the compressor based on the comparison between the voltage difference and the first threshold voltage. The method further comprises counting the period of time during which the voltage difference is less than the first threshold voltage and switching the compressor off when the period of time exceeds a predetermined period of time. The method may also further comprise storing a second threshold voltage in the controller and switching the compressor off when the voltage difference goes below the second threshold voltage. The method further comprises indicating to an operator of the device when the compressor is turned off.
In another embodiment, a method comprises measuring a difference in voltage between the first line voltage and the second line voltage before and during the energizing of the compressor, storing a second threshold voltage in the controller, and controlling operation of the compressor based on the comparison between the voltage difference and the second threshold voltage. The method further comprises switching the compressor off when the voltage difference goes below the second threshold voltage. The method may further comprise indicating to an operator of the device when the compressor is turned off.
While the principal advantages and features of the present invention have been explained above, a more complete understanding of the invention may be attained by referring to the description of the preferred embodiments.